Understanding Memory in Direct Laser Writing

Direct laser writing has, of late, become a widely popular technique for the fabrication of microstructures, and in certain circumstances being preferred to standard lithography techniques due to its dynamic nature in allowing for structure formation without intermediate steps. In this field, a strong emphasis is placed on multi-photon polymerisation, which allows for incredible feature precision. Singlephoton polymerisation has begun to emerge, however, as a significantly less expensive, and thus more accessible, alternative. One limiting factor to this system, however, is its spatial indiscrimination in polymerisation, as reaction initiation needs no more than one photon, and is thus not limited to high photon population areas. Stemming from this complication, aside from a higher limit on feature size due to focal limitations, is a phenomenon we have named the memory effect. Though, in a single-photon system, significant polymerisation limits itself to within a permissible range around the focal point to be able to form structures below single micrometer dimensions, non-hardening oligomerisation seems to occur in the outlier regions of the gaussian beam. This leads to increased subsequent polymerisation in affected areas, enlarging neighbouring structures. Our study sets out to define this effect and variables that may play a role in lessening or even eliminating its consequences